1. Field of the Invention
The present invention relates to a magnetic repulsion type bearing.
2. Description of the Prior Art
Various bearings are in practical use presently, and there may exceed more than 10,000 kinds of bearings if being classified in detail according to the usage and specialty. As long as the function and the way of motion are considered, the bearings can be classified as a roller bearing and a sliding bearing whereas both have their merits and demerits.
If the two are compared with each other, the roller bearing is advantageous for its lower friction, easier to lubricate, capability for supporting both radial and thrust force, fairly better overload capability and well adaptable to the rotating shaft thereby requiring less starting torque, saving less lengthwise space only if the shaft diameter is proper. On the other hand, the roller bearing is disadvantageous for its high price, large operating noise, requiring larger radial space, short lifespan, less ability to withstand vibration without precaution of break down which way be aggravated to destruction of the entire mechanism.
In the meanwhile, the sliding bearing is suitable for a heavy load, low operation speed and impacting machine, whereas the roller bearing is essentially applicable to light load, high operation speed, high precision and non-impacting machine. However, both kinds of bearings have their limits. For instance, friction problem is inevitable to both, and friction not only brings about energy loss and high temperature to deform the machine. As a result, the precision of the products is degraded, even damaging the equipment. The higher the speed, the severer the problem will be. For solving the friction problem, an appropriate lubricant is used to decrease the friction resistance, but the lubricant is easy to contaminate the surroundings or even affect the operation of the bearing.
In all, the traditional surface contact type bearing is unable to get rid of frictional force at all, the mutual frictional contact among the component parts in the machine produces powdered particles from the contact surface which pervading in the air to cause the ambient condition unqualified for high technological industry. For thoroughly solving the friction, the gist of the development is directed to the non-contact type bearing.
The non-contact type bearings which are on the present market can be essentially classified in following three categories:
1. Air bearing: It has the demerits that the working precision degrades as the load increases uncontrollably. Besides, poor rigidity causes it unable to withstand lager load.
2. Fluid bearing: It has the merits of high rigidity to carry larger load with low cost, but the high fluid damping and liable to be affected by temperature degrade its working precision.
3. Magnetic repulsion (suspension) bearing: It is considered to be the most hopeful non-contact type bearing. The working principle is based on the magnetic force. The magnetic suspension force induced by the magnetic field suspends the rotating shaft and prevents contact between the stator and rotor.
As compared with other non-contact type bearings, the magnetic repulsion (suspension) bearing has several noteworthy advantages, namely:
1. No rotational damping force, rotational speed of the shaft is higher than that which uses other bearings.
2. No complicate lubrication or pneumatic means is needed.
3. A long lifespan contributes to lowering maintenance cost.
4. No frictional resistance and noise contributes to maintaining silent and clean environment.
5. Applicable to operate in very low temperature or high vacuum ambient condition such as in the outer space.
6. Assured mechanical rigidity contributes to effectively eliminating vibration in operation.
Although the magnetic suspension bearing has many advantages as described above, it still has several inherent shortcomings, namely:
1. The resistance of the field windings on the electromagnet generates heat when carrying the exciting current results in an energy loss.
2. Low magnetic induction.
3. Severe ineffective divergence of the magnetic flux.
4. Complicated mechanical structure causing difficulty in assembling.
For these defects noticeable on the magnetic repulsion (suspension) type bearing, an improvement is seriously required.